Low B.T.U., high moisture biomass materials are commonly generated in large amounts in the pulp and paper industry. One such material is the wood waste known as hog fuel. This invention is applicable to all such biomass materials, but will be described with particular reference to hog fuel.
The use of wood waste (hog fuel) is considered a very economical method of producing steam at a pulp and paper facility, because of its low cost and ready availability. In order to minimize the use of more expensive fossil fuels, pulp mills having wood burning boilers usually attempt to burn as much hog fuel as possible.
Four presently known methods of combusting hog fuel are:
a) grate firing; PA1 b) suspension firing in combination with grate firing; PA1 c) suspension firing, PA1 d) pulverized and dried suspension firing.
For purposes of illustration this invention is described as applied to one of the above, but it is not intended that it be limited to any specific firing method.
Many of the problems encountered in B.T.U., high moisture content fuels are discussed in such recently issued U.S. Pat. Nos. as the following:
______________________________________ Spurrell 4,235,174 issued Nov. 25, 1980 Lautenschlager 4,250,820 issued Feb. 17, 1981 Rastogi, et al. 4,362,269 issued Dec. 7, 1982 and Kolza, et al. 4,377,177 issued Mar. 22, 1983 ______________________________________
which describe the available fuels and a variety of expedients employed in an effort to overcome the problems inherent in the combustion of such materials. These expedients include predrying the fuel (Spurrell), stagewise introduction of the combustion ar (Lautenschlager and Rastogi) and the provision of an improved grate (Kolza). Each of these and other proposed solutions adds to the expense of carrying out the combustion process and none of them solves all of the difficulties experienced in the process.
Oxygen enrichment of air in combustion processes is known in the art as illustrated by U.S. Pat. Nos. 2,515,545 (D. H. Bangham, et al.) and 4,515,095 (Greskovich). However none of the prior art references describe application of such processes to the combustion of low B.T.U. high moisture content fuel.